U.S. Pat. No. 4,138,041 (COORS CONTAINER COMPANY) describes a gravity infeed through an inclined chute to stationary pockets on a rotatable pocket mandrel wheel. There, the cans are drawn from the pockets and seated by vacuum on mandrels which carry the cans to a printing blanket cylinder.
As it has become important to increase machine speed, a single stack of cans as in the gravity infeed of U.S. Pat. No. 4,138,041 cannot keep up with the speed of the machine, and cannot rely on gravity alone. Air pressure could be used to force the cans downwards but as the speed increases, the use of more air pressure causes can distortion.
Decorating machinery has been employed by companies such as Rutherford and Alcoa in the printing of metal cans. A known 24 mandrel decorator operates at typically 1800 cans per minute (“cpm”) and a 36 mandrel decorator operates at typically 2000 cpm. The single lane infeed of these decorators has been needed to control the speed of the cans and is a limitation of machine production speed.
Conventionally, a continuous stream of cans is fed from conveyor track work into the infeed section of the can body decorator. In a conveyor stack, the can bodies have a linear “pitch” which is the distance between their centres, i.e. one can diameter. Individual cans are separated from the conveyor stack by a pocketed single rotating turret wheel. There are two types of infeed separator turret, constant velocity (‘CV’) and ‘tangential’. The type of feed refers to the point where the can is fed from the conveyor stack onto the infeed separator turret. The challenge for a rotary machine infeed system when feeding cans to any container manufacturing process is that the machine takes delivery of cans which are spaced or “pitched” in a linear fashion and the infeed system must change the pitch between the can bodies to that of a circular turret—and larger pitch.
Following exchange to the separator turret, cans are accelerated up to the peripheral speed of the turret wheel. In known decorators, a further pitch change occurs between the infeed separator turret and mandrel wheel circular pitch. The can body sits in a pocket on this mandrel wheel and is then sucked across using vacuum onto a mandrel. The actual time for this transfer before printing starts is fairly short, especially if the can body is long. The pitch change onto the mandrel wheel has been found to cause can stability problems when misalignment of a can with the corresponding mandrel causes unsuccessful loading. If the can body is not loaded onto the mandrel correctly prior to commencing printing, it has to be blown off. It is apparent that poorly loaded can bodies are rejected and result in spoilage.
Some machine manufacturers omit the infeed separator turret and guide the can onto a profiled “Can Carrier Pocket” which is mounted in front of a mandrel (the mandrel is part of the mandrel wheel), which has the function of changing can conveyor pitch to that of the mandrel wheel circular pitch.
A rotary machine infeed system for a can body die necker is described in WO 2011/113710 (CROWN PACKAGING, INC). However, in this prior art system, the can bodies are always already decorated prior to being necked. The skilled man would not consider trying this necker infeed system for handling the undecorated cans of the present invention because undecorated cans do not convey well at high speeds, since the chemicals used in the can washer upstream of the decorator infeed, affect the surface of the cans. This means that the friction properties will vary—strong etching in the washer causes high friction and the cans do not slide against each other as expected. Use of so-called “mobility enhancer” can help, but it is expensive.
The cans coming into the decorator are “open-ended” or “un-necked” which means that they are not stiff. The cans tend to come into the machine in a long stack of cans which can cause distortion of a can and hang-up on the in-feed guides, and subsequent difficulty in feeding can bodies of unexpected (distorted) shape into the infeed turret. The critical part of an infeed system is when the flexible can body is loaded onto the mandrel. It is therefore desirable that the can body is stable at this point, so as to give minimum spoilage. By having a pitch increase as in conventional infeed systems, the can is not stable and as a result the loading of the can is not 100% reliable.
It is conventional for current decorator turrets at infeed to hold cans in turret pockets by means of vacuum, applied at the can outside diameter.
U.S. Pat. No. 3,613,571 (BROWN MACHINE COMPANY OF MICHIGAN, INC.) describes a container printing machine and method of printing which seeks to provide printing machines capable of running at speeds which may print containers at the rate of as much as 400 cans per minute on each side of a mandrel drum. There is no mention as to how cans are held on the infeed starwheel, nor of any can pitch change through the infeed system.
U.S. Pat. No. 4,048,917 (SUN CHEMICAL CORPORATION) 20, Sep. 1977 is a continuous can printer which is constructed with a worm and star-wheel type input conveyor. Infeed spirals or lead screws such as those described in U.S. Pat. No. 4,048,917 and also U.S. Pat. No. 3,766,851 (SUN CHEMICAL CORPORATION) 23, Oct. 1973, to which U.S. Pat. No. 4,048,917 refers, is old technology and has speed limitations. This is exacerbated by the aspect ratio of some cans. Although U.S. Pat. No. 3,766,851 refers to operation at very high speeds, no actual speed is given and the worm and star-wheel construction of the printer at that time would have prevented its use at line speeds anything like as high as 1000 cans per minute.